Timber Bridges-Design, Construction, Inspection, and Maintenance
1.1 INTRODUCTION
The age of wood spans human history. The stone, iron, and bronze ages were dramatic interims in human progress, but wood-a renewable resource-has
always been at hand. As a building material, wood is abun-
dant, versatile, and easily obtainable. Without it, civilization as we know it would have been impossible. One-third of the area of the United States is forest land. If scientifically managed and protected from natural disasters
caused by fire, insects, and disease, forests will last forever. As older trees are harvested, they are replaced by young trees to replenish the wood supply for future generations. The cycle of regeneration, or sustained
yield, can equal or surpass the volume being harvested.
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